Apparatus for the commutation of direct-current dynamo-electric machines.



No. 788,999. PATENTED FEB. 28, 1905.

G. S. DUNN.

APPARATUS FOR THE OO MMUTATION 0F DIRECT CURRENT DYNAMO ELECTRICMACHINES.

APPLIOATION FILED JUNE 26. 1902. RENEWED SEPT. 12, 1904. I

2 SHEETS-SHEET 1- No. 783,999. PATENTED FEB. 28, 1905. G. S. DUNN.

APPARATUS FOR THE GOMMUTATION 0F DIRECT CURRENT DYNAMO ELECTRICMACHINES.

APPLICATION FILED JUNE 26, 1902. RENEWED SEPT. 12. 1904.

2 SHEETS-SHEET 2.

7 f it;

7376 7'-' Z M jazz UNITED STATES Patented February 28, l 905.

PATENT OFFICE.

GANO S. DUNN, OF AMPERE, NEW JERSEY, ASSIGNOR TO OROOKER- WHEELERCOMPANY, OF AMPERE, NEW JERSEY, A CORPORATION OF NEW JERSEY.

APPARATUS FOR THE COMMUTATION OF DIRECT-CURRENT DYNAMO-ELECTRICMACHINES.

SPECIFICATION forming part of Letters Patent No. 783,999, dated February28, 1905.

Original application filed May '7, 1902, Serial No. 106,318. Divided andthis application filed June 26, 1902. Renewed September 12,

. 1904:. Serial No. 224,179.

To (1,, wltmn it natty concern:

Be it known that I, GANo S. DUNN, a citizen of the United States ofAmerica, and a resident of Ampere, Essex county, New Jersey, haveinvented certain new and useful Improvements in Apparatus for theCommutation of Direct- Ourrent Dynamo-Electric Machines, of which thefollowing is a specification.

The armature coils of direct-current dynamo-electric machines maybedivided into three classes, namely: first, those approaching a brush;second, those receding from a inserted into the path of the currentthrough the receding coils, and the sudden enforcement of thiscorrespondence at the moment the commutator-bar leaves the brush causesa spark or burning of the brush and bar, which generates heat and intime destroys the smooth surface of the commutator, causes abnormalwear, reduces the efliciency of the machine, and makes its operationuncertain.

In the discussion of the various methods of commutation which follows itwill be assumed for simplicity that the current flows from the brushinto the coil under consideration and that the commutator is movingunder the brush from right to left.

There are several means of effecting commutation. Among these areshifting the brushes toward one of the magnetic poles of the machine, sothat the commutation will take place in a region where the coil isinfluenced by the magnetic field. By generating -in a coil while itsterminals are short-eircuited by a brush a local elcctromotive forcethis lield causes the rapid dying out of the current originally flowingand the building up of current in the opposite direction. By the timethe leading terminal is ready to pass out from under the brush theelectrical condition of the coil is so nearly like that of the recedingcoils that at the moment of its being inserted into the path of thecurrent through the receding coils there is no disturbance.

Other means of eltecting connnutation are special 'l'orms of winding,whereby a neutralizing and reversing elcctromotive force is generated inthe leads connecting the coil with the commutator-bars to accomplish thereversal of the commutating-coil, this electromotive force beingproduced by magnets separate from the field-magnets or by carrying alead under one of the poles of the machine in its path between the coiland a commutatorbar.

The above described means and various known modilications thereof allbelong to \v hat 1 term magnetic commutation. The reversal isaccomplished by an elcctromotive force generated in the commutating-coilor some part of its local circuit when shortcircuited by the brush.

There is a second generic method of commutation which 1 call resistancecommutation, since it accomplishes the reversal oi the current in thecommutating-coil by ol'lering alternative paths by which the current mayreach the terminals of the commutatingcoil, the relation of resistancesin these paths being rapidly changed, as the terminals of thecommutating-eoil pass through the region of the brush-contact in suchmanner as to tend to cut off the current entering the leading terminaland to facilitate passage of current from the brush into the trailingterminal of the coil. \Vith substances of high resistivity and contactresistance, as where carbon or graphite brushes are employed, there is astrong throttling efl'ect exerted upon the current passin into theleading terminal of the commutating-coil as the overlap between thebrush and the commutator-bar of the leading terminal is diminished whichtends to cut off current from going into the bar of the leadingterminal, and thereby to establish the full amount of the normal currentin the coil from the bar connected with the trailing terminal before thebar connected with the leading terminal of the coil passes out ofcontact with the brush. At the moment, therefore, when the leadingterminal of the coil is disconnected from the brush and the coil isinserted into the path of the current through the receding coils thereis no troublesome shock.

Most direct-current dynamo-electric machines at present in use commutateby combined magnetic and resistance methods.

For reasons that it is not necessary to enumerate the limit ofcommutation by these methods or combinations thereof has practicallybeen reached,or, in other words, the limit of electrical inertia orinductance that can be overcome by commutation has been reached. Thisnecessitates that the designing of directcurrent machines for highervoltages than are now commonly employed therewith must proceed alonglines of such alteration in present proportion that while the voltage isincreased the inductance shall not be permitted to rise above valuessuch as can be succcssfullycommutated by means known to the art at thepresent time. This tends to extravagance in certain proportions of themachinery and not only renders its cost out of proportion to itsperformance, but beyond a certain point renders the constructionimpracticable. No suitable substance has been found the resistivity andcontact resistance of which is higher than that of carbon and itsmodifications, and the prospects of development along this line are notpromlsmg.

My invention without diminishing the value of magnetic commutationincreases indelinitely the effectiveness of resistance commutation, sothat much higher voltages than are now commonly employed withdirect-current dynamo-electric machinery can be successfully employed.It also enables very impm'tant changes to be made in the structure ofmachines attended by reduction of cost.

The method disclosed in this application is claimed in a copendingapplication filed May 7, 1902, Serial No. 106,318, of which the presentapplication is a division.

My invention consists of a commutator .brush made up of a live brush anda number of dead brushes at one side of the live brush and operating inconjunction therewith.

1 have shown the invention applied to simple multiple circuit or loopwindings; but it is equally applicable to what are known as twocircuitor wave windings and to the various modifications of each of theseclasses of windings.

1n the accompanying drawings, which form a part of my specilicatioi'i,Figure 1 is a side i l l close them.

elevation showing portions of a commutator and a ln'ush-holder with myimproved brush applied. Fig. 2 is a plan view of the same parts. Fig. 3is a plan view of a modification in which the insulation between thedead brushes is slanting with respect to the commutator-bars. Fig. at isa side view of a further modification in which the brushes overlap oneanother. Fig. 5 is a plan view of the same, and Fig. 6 is a diagramshowing approximately the operation of the invention.

Referring to Figs. 1, 2, and 3, the commutator A is supposed to revolvein the direction of the arrow. The brush-holder B, of any suitableconstruction, supports a brush in its socket C. The ordinary brush 1),of carbon or graphite or other suitable material. is supported in thesocket as usual, so as to form electrical contact with the commutatorhars 6, connected with the commutatingcoils (Z. hown only in Fig. (5.)Located in the socket C on the trailing side of the live brush l) is aplurality of brushes E, of carbon or graphite or other suitablematerial, which are insulated from each other and from the live brush bysuitable insulation F, such as sheets of mica, paper, or equivalentinsulation, that may be wrapped around the brushes F1 so as to in- Thebrushes E are insulated not only from the live brush and its holder, butfrom every other part of the l'nz'ichinc, so that they are completelydead except for their contact with the commutator-bars. Hence they arecalled dead brushes.

. The progress of a coil in connnutation by my method--that is to say,the electrical connections and condition of a coil as it occupiessuccessively the positions of coils a, 1,, 2, 3, 1, 5, 6, 7, and r 'willnow be discussed.

Referring to the diagram Fig. (i, coil (1. is receiving current from itsleft-hand or leading terminal, which flows out at the right-hand ortrailing terminal and into the coils to the right. The direction andstrength of this current are thesame as that which is in theneighborii'ig approaching coils. \Vhen the coil (1. reaches the positionof the coil 1. it is shortcircuited through the live brush; but owing toits inductance current continues to flow in the same direction asbefore, although of a diminished value. When the coil a reaches position2, it is shm't-circuited through adead brush. its advancing terminal isconnected to the live brush 1) through the dead brush E, and itstrailing terminal is connected to the live brush 1) directly and alsothrough coil 1. In each of these three conl'iections there is onebrush-to-eommutator contact from the live brush. Since the contactbetween the live brush and the commutator is common to all of thecircuits shown in the drawings, it will not-be further referred to. Alsowhile the neutral point is shown as at position 1-1 it may be locatedfarther to the right or to the left.

Considering now coil 1/ when in position 2,

current tends to flow from the live brush in at the trailing terminal;but this, which would effect a reversal of the coil, is opposed by theself-induction thereof. Current also tends to flow from the live brushand in at the leading terminal; but this is opposed by the twoadditional surface contacts between the commutator-bar and the firstdead brush and this brush and the next eommutator-bar. As the coil Itmoves to the left the number of these surface contacts between the livebrush and the leading terminal increases step by step, there being twoadded contacts for each dead brushthat is, the facility of receivingcurrent at the leading terminal is progressively diminished because ofthe increasing number of contact-surfaces through which such current hasto pass. On the other hand, the facility of receiving current at thetrailing terminal from the coils to the right is not diminished. Thistends to reverse the coil gradually or in steps corresponding to thenumber of dead brushes. This I term fractional commutation.

In order to obtain full benefit of the dead brushes, their pitch shouldbe approximately that of the commutator-barsthat is to say, the distancebetween the centers of the dead brushes should be practically thatbetween the centers of the cominutatorrbars. If, for example, the pitchof the dead brushes should be half that of the commutator-bars, therewould be positions where two dead brushes cover one bar and only onepair of contactsurfaces would be effective instead of two. If the pitchof the dead brushes were intermediate between one-half of the pitch andthe full pitch of the commutator-bars, then a portion of thebrushes-less than half-would be rendered useless in certain relativepositions of the conimutator-bars and the brushes. The case is similarif the brush-pitch exceeds the bar-pitch.

To state concisely my method of commutation, it may be said that whenthe coil is shortcircuitcd through the brush there is a moment at whichthe contact resistance is balanced at the two terminals of the coil andthat the resistance is thereafter progressively increased on one sideand not increased on the other that is to say, after the moment at whichthe resistance is balanced at the two terminals of the coil theresistance at the leading terminal is progressively augmented by theaddition of contact resistance while the inductive reactance of thecoils is dying away. In this way a path of current with maximumresistance is formed which departs from and returns a mul tiplicity oftimes into the commutator-sur face. By following the pitch described Iam enabled to extend this elfect indefinitely. An effect to be noted dueto this method of commutation is that not only into the advancingterminal of one but into the advancing terminals of a number ofsuccessive coils a graduallyincreasing resistance is introduced in sucha way that at each terminal a resistance of different amount to that atany other terminal is produced at a given time, forming as many paths ofcurrent as there are different resistances. I

It will be understood that each dead brush may be compound that is,composed of a number of non-insulated parts.

In Fig. 3 the planes of separation between the brushes are inclinedrelatively to the planes of separation between the commutatorbars forthe purpose of preventing an instant of absolute rupture of thecommutating-current when the trailing side of the live brush leaves thecomm utator-bar, thereby avoiding a spark or burning of the bar. Anotheralter native means for accomplishing this end is shown in Figs. 4 and 5,in which the dead brushes are arranged in two series y la, the brushesbeing also staggered relatively to each other, so that a dead brush inone series partly overlaps a dead brush of the other series, while thelive brush is divided into two parts, one being thicker than the other,so that one of the dead brushes may partlyoverlap it. Each series ofdead brushes is not only insulated from the other series, but theindividual dead brushes are insulated from each other, as in the mainform of the invention.

it is obvious that for reversing motors dead brushes will be located atboth sides of the live brush.

Without limiting myself to the details shown, what I claim, and desireto secure by Letters Patent of the United States, is

A commutator-brush made up of a live brush and a number of dead brushesat one side of the live brush and operating in conjunction therewith,substantially as described.

Signed by me at Ampere, New Jersey, this 20th day of June, 1902.

GANO S. DUNN.

l/Vitnesses:

F. V. HuNsnAw, H. J. FULLER.

